Microbial nanowires with increased conductivity and reduced diameters

Abstract

Improved electrically conductive pili were generated from a natural pilus protein from the microorganism Geobacter sulfurreducens. Substituting a tryptophan for the phenylalanine at position F51 and a tryptophan for the tyrosine at position Y57 of the pilus monomer substantially increased the conductivity of the pili and reduced their diameter to 1.5 nm. Substantial improvements in conductivity were also achieved by substituting an additional tyrosine, histidine, and phenylalanine in the pilus monomer to mimic the monomer of Geobacter metallireducens, but the pili retained the typical Geobacter sulfurreducens wild-type diameter of 3 nm.

What is claimed is: 
     
       1. An electrically conductive pilus comprising a plurality of modified  Geobacter sulfurreducens  PilA monomers, wherein each modified PilA monomer comprises an amino acid sequence that differs from SEQ ID NO: 19, the amino acid sequence of the wild-type  Geobacter sulfurreducens  PilA monomer, by the substitution of at least the amino acids at positions F51 and Y57 of SEQ ID NO: 19 with tryptophan, and wherein the electrically conductive pilus has greater conductivity than a wild-type  Geobacter sulfurreducens  pilus. 
     
     
       2. The electrically conductive pilus of  claim 1 , wherein one or more amino acids at positions F24, Y27 and Y32 of SEQ ID NO: 19 are additionally substituted with tryptophan in each modified PilA monomer. 
     
     
       3. A method of making the electrically conductive pilus of  claim 1 , comprising the steps of: providing a microorganism capable of producing a pilus; modifying a DNA sequence of said microorganism to encode a modified PilA monomer that comprises an amino acid sequence that differs from SEQ ID NO: 19 by the substitution of at least the amino acids at positions F51 and Y57 of SEQ ID NO: 19 with tryptophan; growing a quantity of said microorganisms; and harvesting at least one electrically conductive pilus from said quantity of grown microorganisms. 
     
     
       4. The method of making an electrically conductive pilus of  claim 3 , wherein said microorganism is  Geobacter sulfurreducens.    
     
     
       5. The method of making an electrically conductive pilus of  claim 3 , wherein substituting the DNA sequence encoding tryptophan in the PilA monomer comprises substituting a sequence from a different microorganism. 
     
     
       6. A method of using the electrically conductive pilus of  claim 1 , comprising the steps of: providing a microorganism capable of producing a pilus; modifying a DNA sequence of the microorganism to encode a modified PilA monomer that comprises an amino acid sequence that differs from SEQ ID NO: 19 by the substitution of at least the amino acids at positions F51 and Y57 of SEQ ID NO: 19 with tryptophan; growing a quantity of said microorganisms; harvesting at least one electrically conductive pilus from said quantity of grown microorganisms; placing at least one of the harvested electrically conductive pilus between a pair of conductive terminals, and applying an electrical signal between said pair of electrical terminals to cause said at least one electrically conductive pilus to provide a current-voltage response. 
     
     
       7. The method of using an electrically conductive pilus of  claim 6 , wherein said microorganism is  Geobacter sulfurreducens.    
     
     
       8. The method of using an electrically conductive pilus of  claim 6 , wherein substituting the DNA sequence encoding tryptophan comprises substituting a sequence from a different microorganism. 
     
     
       9. The electrically conductive pilus of  claim 1 , wherein the pilus has a diameter of less than 3 nm. 
     
     
       10. The electrically conductive pilus of  claim 9 , wherein the pilus has a diameter of about 1.5 nm. 
     
     
       11. The electrically conductive pilus of  claim 1 , wherein the pilus is about one million-fold more conductive than a wild-type  Geobacter sulfurreducens  pilus.